Explorations: An Introduction to Astronomy (Arny), 7th Edition

Chapter 17: Galaxies

Thought Questions

1
Hubble proposed that his tuning-fork diagram might represent evolutionary changes with E galaxies gradually changing to S galaxies. What evidence based on the amount of interstellar matter and kind of stars in E and S galaxies indicates that this is very unlikely?
2
Take a look at an egg from different angles. Do you think the classification of elliptical galaxies is always accurate? Examining figure 17.8, could an E0 be mistaken for an E7, or an E7 for an E0? Explain why there is or is not a similar problem for identifying spirals. What does this imply about the actual number of each type compared to what is observed?
3
The value of the Hubble constant was only recently determined to high accuracy. If H were equal to 100 km/ (sec Mpc) instead of H = 70 km/sec/Mpc, as some astronomers thought it would be, how many times larger or smaller would the distance to a distant galaxy be? How much larger or smaller would the diameter of the galaxy be?
4
If you wanted to look at your mother when she was a baby, how far out in space would you need to be? (Assume you have a sufficiently powerful telescope and pretend that you can travel instantly to any distance.) What if you wanted to look in on astronomers in ancient Egypt around 3000 b.c.? How does this relate to astronomers studying young galaxies?
5
Explain how selection effects might make it difficult to obtain an accurate census of galaxy types. What might happen at near and far distances? What about if you picked an area in the middle of a super cluster, or an area in a void? (You don't know what's there until you look!)
6
Are the jets that come out of active galaxies similar to bipolar outflows? Explain your answer.
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